Re: [ATM] Astigmatism in round robin mirror C with Foucault.

[Dale Eason <atmpob@yahoo.com>]

I have mirror C.  I have too many other things I want
to try first.  But what I do have are a sequence of
Foucault Images taken at known roc offsets with no
mask.  If anyone wants to analyze those images I can
post them somewhere.  It is several megabytes.  I
forget the step size but is something like about every
.005 inch.  I also have ronchi images taken every .05
inches from -.3 to .3  ROC for both 100 and 150 LPI
screens.  I want to post those somewhere as well.  I
would like to put them on the ATM site but I haven't
looked into how to get that to happen.

What I'm going to do tonight is take the rond robin
measurements from both diagonals compute surface
profiles like I have been doing.  Then I will do a
least square Zernike fit to both diameters and see
what I come up with.

Dale Eason
--- Nils Olof Carlin <nilsolof.carlin@telia.com>
wrote:

> One way of doing a feasibility test is to use Jim
> Burrpows' Diffract to
> simulate the test in question - it will allow quite
> a variety of
> possibilities, and simulate astigmatism (wish I knew
> what those Zernike term
> suffixes mean ;-) and see what happens - with a
> certain RMS value (shown) of
> astig, and the axes aligned where they should be, if
> you can't detect astig
> in the simulation, you are not likely to do so in
> reality.
> It seems to me that the "steel ball" test of
> Texereau (p 86 in my edition)
> may work for a spherical mirror, but is essentially
> useless for any
> practical paraboloid.
> 
> One method that might work, I believe without having
> tried, is a Foucault
> test with a Couder mask with 2 rows of openings
> arranged in an "X" fashion -
> you match the diagonally opposite openings of each
> arm (make top and bottom
> of each opening "horizontal", i.e. at right angle to
> the KE). If astig is
> present, the readings along "/" and "\" directions
> would differ, and
> hopefully you could use sixtests to get the
> difference of radii with
> reasonable precision, although a little less than
> with a conventional test -
> repeating this after turning the mirror, hoping to
> find the position where
> the axes of astigmatism are aligned to produce the
> maximum effect.
> 
> Anyone with a known astigmatic mirror lying around?
> 
> Nils Olof
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



		
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